1. Field of the Invention
The present invention relates to a boring tool or drilling bit, preferably for use in a hammer drill. The drilling bit has a drilling head, a shaft portion connected thereto, an insertion or chucking part for connection with a driving unit, and at least one, preferably two, helical withdrawal flutes or grooves which extend from the drilling head.
2. Description of the Prior Art
With heretofore known drilling bits of this type, the withdrawal groove, which is provided for removal of the cuttings and dust produced during drilling, has a constant slope over its entire length. When used in a hammer drill, axial impacts or strokes overlap the rotational movements of the drilling bit and act upon the chucking end of the bit. Longitudinal oscillations are produced in the drilling bit as a result of these stroke pulses. The pulse wave front resulting from the continuous pulse stress is reflected in part at cross-sectional jumps of the drilling bit. These jumps are produced by the withdrawal groove, in the vicinity of which the drilling bit has a reduced cross section. Since the withdrawal groove of the heretofore known drilling bit has a constant slope, the cross-sectional jumps are disposed at uniform intervals along the bit. As a result, the pulse wave front is continuously partially reflected at each cross-sectional jump. However, this continuity affects the transverse oscillations, which share responsibility for noise, which are finally also stimulated by the stroke pulses, and which can be reinforced by the partially reflected pulses. As a result of the cross-sectional jumps being disposed at uniform intervals, resonance oscillations can even occur, due which the drilling bit is stressed very severely, and can even become damaged. The transverse oscillations, which are reinforced by the partially reflected pulses, result in the development of considerable noise. Furthermore, the drilling power of the bit is reduced due to the partially continuous reflection of the longitudinal oscillations.
It is an object of the present invention to design a drilling bit of the aforementioned general type in such a way that the energy of the stroke pulse is distributed in the drilling bit in such a way that the bit obtains a greater chip-producing or material-removing energy, while the noise or sound energy is reduced.